1. Field of the Invention
The present invention relates to a composition for removing photoresist and to a method of forming a bump electrode in a semiconductor device using the composition. More particularly, the present invention relates to a composition characterized by a simplified formulation and the effective removal of photoresist, and to a method of forming a bump electrode in a semiconductor device using the composition.
2. Description of the Related Art
To facilitate mounting of a packaged semiconductor chip having multiple pins on a printed circuit board of an electric or electronic device, the packaged semiconductor chip is preferably constructed to have a relatively low height. The packaged semiconductor chip generally includes a connection device such as a bump electrode which extrudes from the packaged chip by more than about 20 μm. As a highly integrated semiconductor chip is generally required, the bump electrode should have precise dimensions and structural characteristics.
The bump electrode may be formed in the semiconductor device by a process such as an electroplating process, a vacuum evaporation process or a stirred process using a wire bonding. The electroplating process is relatively simple and economical, and thus is widely used.
In the electroplating process, a passivation layer pattern is formed on a substrate having a metal wiring formed thereon to expose a bump electrode contact region of the metal wiring. A seed layer or a metal base layer is formed in the bump electrode contact region to electroplate metal for the bump electrode. A photoresist pattern is formed on the substrate including the bump electrode contact region where the bump electrode is formed. The bump electrode contact region is filled with the metal for the bump electrode. The photoresist pattern is then removed to complete the bump electrode. Here, the photoresist pattern is preferably thicker than a height of the bump electrode. Thick photoresist, which results in a photoresist layer having a thickness greater than about 5 μm, may be used to form the photoresist pattern. The thick photoresist should have a high adhesive strength relative to the substrate, a high plating solution resistance and a high wettability against the plating solution. Additionally, photoresist that can be easily detached from the substrate is preferable.
Since the photoresist pattern is relatively thick, the bottom portion of the photoresist pattern may not be exposed in an exposure process. When the photoresist pattern is removed by a subsequent ashing process, the photoresist pattern may be damaged by plasma used in the ashing process. In a subsequent stripping process, some of the photoresist pattern may reside between bump electrodes, thereby resulting in a failure of the semiconductor device.
In the stripping process, a composition used as a stripper dissolves the photoresist pattern, and then detaches the photoresist pattern from the substrate to remove the photoresist pattern. When the stripper fails either in dissolving or detaching of the photoresist pattern, the photoresist pattern may remain on the substrate. This also occurs when the stripper may not be mixed with water. Most organic stripper compositions are suitable for removing a polymer. When the stripper is used for removing the photoresist for forming the bump electrode, the photoresist may not be completely stripped or be recoated on the substrate. Hence, two kinds of stripper have been used, and a stripping process has been performed twice using each stripper. This increases the processing time.
A thinner composition may also be used for removing the photoresist. The thinner composition may process a semiconductor substrate by one sheet. When the thinner composition is used for processing a plurality of substrates at the same time, remainder of the photoresist pattern may reside on the substrate, thereby diminishing process efficiency.
Use of monoethanolamine as a solution for stripping photoresist is disclosed in U.S. Pat. No. 5,798,323 (issued to Honda et al.). Honda et al. discloses a composition including monoethanolamine to strip photoresist. Although the composition is proper for stripping a thin photoresist film having a thickness of about several microns, the composition may not be suitable for stripping a thick photoresist film.
Japanese Patent Laid Open Publication No. 1997-283,508 discloses a solution including monoethanolamine and dimethylacetamide for stripping polyimide. This Japanese Patent Publication also discloses a method of stripping an undesired polyimide layer using monoethanolamine and dimethylacetamide. The composition for stripping photoresist employed for forming a bump electrode, however, is not mentioned in the Japanese Patent Publication.